Fix icom.c logic to not reject good answers

https://github.com/Hamlib/Hamlib/issues/596

rigs/icom/frame.c

@@ -279,6 +279,8 @@ int icom_one_transaction(RIG *rig, int cmd, int subcmd,
 
     if (NAK == buf[frm_len - 2]) { RETURNFUNC(-RIG_ERJCTED); }
 
+    if (ACK != buf[frm_len - 2]) { RETURNFUNC(-RIG_BUSBUSY); }
+
     *data_len = frm_len - (ACKFRMLEN - 1);
     rig_debug(RIG_DEBUG_TRACE, "%s: data_len=%d, frm_len=%d\n", __func__, *data_len,
               frm_len);

rigs/icom/icom.c

@@ -3081,14 +3081,7 @@ int icom_get_level(RIG *rig, vfo_t vfo, setting_t level, value_t *val)
         lvl_len--;
     }
 
-    if (lvl_len >= 1 && lvlbuf[0] != ACK && lvlbuf[1] != NAK)
+    if (lvlbuf[0] != lvl_cn)
-    {
-        //  if we don't get ACK/NAK some serial corruption occurred
-        // so we'll call it a timeout for retry purposes
-        RETURNFUNC(-RIG_ETIMEOUT);
-    }
-
-    if (lvlbuf[0] != ACK && lvlbuf[0] != lvl_cn)
     {
         rig_debug(RIG_DEBUG_ERR, "%s: ack NG (%#.2x), len=%d\n", __func__,
                   lvlbuf[0], lvl_len);
@@ -3211,11 +3204,13 @@ int icom_get_level(RIG *rig, vfo_t vfo, setting_t level, value_t *val)
         {
             val->f =
                 rig_raw2val_float(icom_val, &icom_default_rfpower_meter_cal);
+            rig_debug(RIG_DEBUG_TRACE, "%s: using rig table to convert %d to %.01f\n", __func__, icom_val, val->f);
         }
         else
         {
             val->f =
                 rig_raw2val_float(icom_val, &rig->caps->rfpower_meter_cal);
+            rig_debug(RIG_DEBUG_TRACE, "%s: using default icom table to convert %d to %.01f\n", __func__, icom_val, val->f);
         }
 
         break;

rigs/icom/icom.h

@@ -30,7 +30,7 @@
 #include <sys/time.h>
 #endif
 
-#define BACKEND_VER "20210306"
+#define BACKEND_VER "20210310"
 
 /*
  * defines used by comp_cal_str in rig.c